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In this study, the mechanical properties of aluminum vibration damping sheet and 1.5 GPa HPF steel sheet (SABC1470) dissimilar joining were evaluated. Joint methods of self piercing rivet (SPR), bolt/nut, flow drill screw (FDS), and blind rivet were compared to evaluate joint characteristic. In SPR Joining, buckling failure was occurred in SPR rivet caused by the strength of the 1.5 GPa HPF steel. So that, SPR hybrid joining was selected with a Al5052 alloy additional plate in lower sheet for formability and pre-hole processed on 1.5 GPa HPF steel in upper sheet. Through optimized of SPR die, the tensile shear load of the SPR hybrid joining was measured 7.53 kN. In FDS joining, failure of fastener was occurred due to the high strength of the 1.5 GPa HPF steel. FDS joining was available after pre-hole process on the 1.5 GPa HPF steel. However, delamination of the aluminum damping plate was observed and the tensile shear load was measured 3.14 kN. In bolt/nut joining, tensile shear load was measured depending on process variable (combination of plate, washer and tightening torque) and maximum tensile load was measured 5.43 kN. In blind rivet joining, the maximum tensile shear load was measured 3.64 kN, when the Al vibration damping sheet was placed on the upper plate. The large area of the blind rivet head released the concentration of stress on Al vibration damping sheet. As a result, SPR hybrid joining is considerable method because pre-hole processing is minimized and tensile shear load is higher than the other method.

The necessity of dissimilar joining between aluminum alloy and steel is increasing in order to meet the demand for weight reduction in automobiles. However, dissimilar joining between 7000 series aluminum alloy and steel is challenging with mechanical joining methods such as self-piercing rivet(SPR) and flow drill screw(FDS) without hole processing. In this study, mechanical performances of dissimilar joints between 3 mm thick Al7075-T6 and 1 mm thick SPFC590DP were evaluated for use in lightweight B-pillar assembly. Self-Piercing Rivet(SPR) and Flow Drill Screw(FDS) with one-hole processing, bolt/nut and blind rivet with two-hole processing and adhesive bonding were compared with respect to joint performance. In SPR joining, rivet did not penetrate and rivet buckling occurred in the rivet due to the thickness and high strength of the Al7075-T6. By processing pre-hole on Al7075-T6 and applying an additional Al5052-H32 sheet to induce mechanical interlock in SPR joint, it became possible to join Al7075-T6 to SPFC590DP with an SPR. The tensile shear load of the SPR joint was 9.8 kN. In FDS joining, it is also necessary to process pre-hole on Al7075-T6 since the fastener could not penetrate the Al7075-T6. The tensile shear load of the FDS joining was 8.1 kN. In bolt/nut and blind rivet joining, the tensile shear load were measured respectively 11.1 kN and 5.2 kN. In adhesive bonding with 1K glue, the tensile shear load was measured 18.5 kN when the interfacial surface was roughened with a sand paper.

An electrospun nanofiber membrane significantly improves the electrical performances of triboelectric nanogenerators (TENGs) due to its high surface area. In recent years, composite nanofibers were applied to a TENG using various electrospinning system types to further enhance the performance of TENGs; however, the effects of the systems on the energy harvesting capability of TENGs have not been investigated thoroughly. This study aims to fabricate polyimide/poly(vinylidene fluoride-co-trifluoroethylene) composite nanofiber-based TENGs with three different nozzle systems: single nozzle, conjugated nozzle, and multinozzles, and two different collectors: plate collector and drum collector. A TENG with multinozzle-drum system-based nanofibers produced an output voltage of 364 V, a short-circuit current of 17.2 μA, a transferred charge of 29.72 nC, and a power density of 2.56 W/m2 at a load resistance of 100 MΩ, which were ∼7 times higher than those of other system-based nanofibers. Under the 10,000 cycles of loading, the TENG stably harvested electric energy. The TENG could also harvest energy from the human body motions, and it is sufficient to illuminate 117 light-emitting diodes and drive several electronic devices. The proposed TENG exhibits excellent electric performances as a wearable energy harvester.

In the hemodynamic study, computational fluid dynamics (CFD) analysis has shown that high wall shear stress (WSS) is an important parameter in cerebral aneurysm formation. However, CFD analysis is not more realistic than fluid–structure interaction (FSI) analysis given its lack of considering the involvement of vascular structures. To investigate the relationship between the hemodynamic parameters and the aneurysm formation, the locations of high WSS and high strain were extracted from the CFD and FSI analyses, respectively. Then the distances between the aneurysm formation site and the locations of high WSS or high strain were calculated. A total of 37 intracranial paraclinoid aneurysms were enrolled for quantitative comparison. Additionally, the dura mater was modeled to facilitate realistic results in FSI analysis. The average distance from the location of the aneurysm formation site to the high strain (1.74 mm $$\pm $$ ± 1.04 mm) was smaller than the average distance to the high WSS (3.33 mm $$\pm $$ ± 1.18 mm). The presence of dura mater also influenced the findings in the aneurysm formation site. High strain extracted by FSI analysis is an important hemodynamic factor related to the formation of cerebral aneurysms. Strain parameter could help to predict the formation of aneurysms and elucidate the appropriate treatment.

An optimum design methodology for a large area, flexure-based XYθ mask alignment stage, which can be applied to a 12-inch wafer photolithography process, was presented. The XYθ micropositioning stage consisted of a working plate with a 12-inch hole in the center, three piezo actuators, and three displacement amplifiers based on the bridge-type flexure mechanism. Grey relation analysis and orthogonal array were incorporated with finite element analysis to find optimum design conditions. The grey relation grade with weight factors was used to simultaneously optimize three objective characteristics of the micropositioning stage: the maximum stroke, deflection of the working plate, and first natural frequency. The optimally-designed stage was fabricated by wire electrical discharge machining and tested to investigate its performance. The proposed stage showed the first natural frequency of 57 Hz and the maximum stroke of 122.84 μm, 108.46 μm, 0.685 mrad in the x-, y-, and θ-direction, respectively. The resolutions in corresponding directions were 11 nm, 10 nm, and 0.5 μrad. The performance of the stage was improved by optimum design process, and the experimental results were in good agreement with the predicted ones from the finite element analysis.

In this study, the effects of various fabrication parameters on the electrical performance of an electrospun nanofiber-based triboelectric nanogenerator (EN-TENG) are systematically investigated through the design of experiments. We selected four fabrication parameters to examine, namely: (i) working distance (needle to collector distance), (ii) needle gauge, (iii) electrospinning time, and (iv) counter materials. A mixed orthogonal array of L18 experiments was designed with respect to the one factor having two level values and three factors having three level values. The open circuit voltage of the EN-TENG was varied from 86.1 to 576.7 V with the aforementioned fabrication parameters. A longer working distance, a larger needle gauge, and a longer electrospinning time increased the open circuit voltage. The power density of the optimized EN-TENG was approximately 2.39 W/m2 at a 100 MΩ load resistance and was sufficient to illuminate a total of 200 LEDs.

This study aims to improve the sensitivity of sensors using porous structures and cone-shaped patterns in the composition of a capacitive pressure sensor. A simple and rapid fabrication method for the production of porous structures and cone-shaped patterns using microwave irradiation of emulsions containing polydimethylsiloxane (PDMS) and a sacrificial solvent is introduced in this study. Through this method, a porous PDMS dielectric layer could be simply fabricated within a few minutes. The sensitivity was greatly improved by both enhancing deformability and increasing the dielectric constant under the external pressure. The effect of pattern distance was investigated, and the sensor with the pattern distance of 600 μm showed a remarkably high sensitivity of approximately 5 kPa−1. Moreover, the effect of aspect ratio and sharpness of the patterns were also studied through a finite element analysis. Finally, we demonstrated the performance of the sensor using a sensor array and finger attached sensors, and they showed sufficient performance for use in wearable devices applicable to artificial skin, surgical robots, and pressure monitoring systems, among others.

Surface modification of polyimides (PIs) using electrospinning would significantly improve the performance of TENGs because of the larger surface area of the electrospun friction layer. However, PIs generally have high solvent resistance, so it is complicated to convert them into nanofibers using electrospinning process. This study aims to fabricate PI nanofibers via simple, one-step electrospinning and utilize them as a friction layer of TENGs for better performance. PI nanofibers were directly electrospun from PI ink made of polyimide powder without any additional process. The effect of PI concentration on spinnability was investigated. Uniform and continuous nanofibrous structures were successfully produced at concentrations of 15 wt% and 20 wt%. Electrospun PI nanofibers were then utilized as a friction layer for TENGs. A TENG with 20 wt% produced an open circuit voltage of 753 V and a short circuit current of 10.79 μA and showed a power density of 2.61 W m−2 at a 100 MΩ load resistance. During tapping experiment of 10,000 cycles, the TENG could stably harvest electrical energy. The harvested energy from the proposed TENG is sufficient to illuminate more than 55 LEDs and drive small electronic devices, and the TENGs exhibit excellent performance as a wearable energy harvester.

The objective of this work is to establish a volumetric metal 3-dimensional (3D) printing system based on material extrusion method and to fabricate metal patterns by investigating various process variables. Numerical heat transfer simulation was conducted to design the nozzle system with a minimized heat loss at the nozzle tip. Based on the simulation results, a metal 3D printing system with X, Y, and Z stages was constructed. The effects of lead content in molten metals and printing conditions such as stage speed and flow rate were investigated. The line formation like bulged, uniform, and dashed lines was evaluated using an optical microscope, and the variation in line widths of uniform lines was investigated with the process variables. Various types of 2-dimensional (2D) patterns were fabricated with an optimized process variable. A simple 3D structure was obtained to demonstrate the feasibility of the proposed system and procedure.

The fatigue life of the resistance spot weld of 980 MPa grade transformation induced plasticity (TRIP) steel was investigated and failure modes and fracture surfaces according to the fatigue load were analyzed. The fatigue life according to the nugget size was observed by using two electrodes with face diameters of 8 mm and 10 mm. When an electrode face diameter with 10 mm was used, the nugget size was large, and the fatigue life was further increased. After the fatigue test, three types of failure modes were observed, namely pull-out, plug, and heat affected zone (HAZ) failure, depending on the fatigue load. The fracture surfaces in each failure mode were analyzed. In all failure modes, a crack was initiated in the HAZ region, which is the interface between the two materials in all failure modes. In the case of pull-out failure, the crack propagates as if it surrounds the nugget at the outer edge of the nugget. In the case of HAZ failure, the crack propagates in the thickness direction of the material and outward in the nugget shell. Plug failure occurs with pull-out failure and HAZ failure mixed. The propagation patterns of cracks were different for each failure mode. The reason why the failure mode and the fracture surface are different according to the fatigue load is that the propagation speed of the fatigue crack is fast when the fatigue load is relatively large and is slow when the fatigue load is low.

The aim of this study is to design and test a new, simple, and reusable linear variable differential transformer (LVDT)-based in situ bolt preload monitoring system (L-PMS) during fastening of a truck wheel assembly. Instead of measuring the elongation of a bolt, the distance between the end surfaces of both the bolt and nut was monitored via the L-PMS. The distance obtained from the L-PMS was experimentally correlated with the actual preload measured by a washer-type load cell. Since the variation of the distance is related to the stiffness of the bolt and clamped parts, a finite element analysis was also conducted to predict the sensitivity of L-PMS. There was a strong linear relationship between the distance and bolt preload after the bolt and nut were fully snugged. However, a logarithm-shaped nonlinear relationship was irregularly observed before getting snugged, making it difficult to define a clear relationship. In order to tackle this issue, an arc-shaped conductive line was screen-printed onto the surface of the clamped parts using a conductive carbon paste. The results show that a resistance variation of the conductive line during fastening enables to determine the snug point, so the L-PMS combined with resistance measurement results in an approximately &plusmn, 6% error in the measurement of bolt preload. The proposed L-PMS offers a simple but highly reliable way for measuring bolt preload during fastening, which could be utilized in a heavy-truck production line.

Pressure sensors for wearable electronics are mounted on irregular surfaces and exposed to various external stimuli. Therefore, the sensor should have a flexible structure and wide pressure measurement range along with high sensitivity. In this study, we fabricated hierarchically porous structured polydimethylsiloxane (PDMS) composites with a simple and cost-effective method using sugar particles and a water-in-oil emulsion. Hierarchically porous PDMS composites were employed as the dielectric layers of flexible capacitive pressure sensors. The capacitive pressure sensor presents a sensitivity 22.5 times higher (0.18 kPa−1) than the sensors using bulk PDMS with a wide measurement range (0–400 kPa). The finite element analysis was implemented to analyze the non-linearity of sensors by observing the compressive behavior of the PDMS composites. For the practical applications, finger attached-sensor, respiration monitoring system, and sensor array were tested, and the proposed sensors showed sufficient potential for application in wearable electronics.

In this study, we develop a simple and low-cost surface wettability patterning based on soft lithography processes such as nano-imprint lithography (NIL) and micro-contact printing (μCP) to fabricate high-resolution conductive patterns using two different solution processes: inkjet printing and spin coating. An epoxy-based photoresist layer was imprinted by an elastomeric stamp during the NIL process to produce negative micro-structures in the epoxy-based photoresist layer. To form surface wettability contrast, a hydrophobic fluorocarbon film was transferred onto the top surface of the imprinted epoxy-based photoresist layer using μCP. The epoxy-based photoresist layer was UV-treated before the μCP process in order to increase surface wettability contrast; the hydrophilic imprinted patterns surrounded by hydrophobic surfaces were fabricated in the epoxy-based photoresist layer. After printing Ag ink on the imprinted epoxy-based photoresist layer, high-resolution printed line array and square spiral patterns with line width and gap distance of several micrometers can be fabricated with an aid of high surface wettability contrast. Even though well-defined high-resolution conductive patterns with electrical resistivity lower than 6 μΩ cm can be obtained regardless of the solution processes, inkjet printing seems more efficient from the viewpoint of the amount of ink used in each solution process. The surface wettability patterning suggested in this study is expected to be used in the fabrication of high-resolution conductive patterns in printed electronics.

Even though porous elastomers and elastomeric nanocomposites have shown many advantages for triboelectric nanogenerators (TENGs), their fabrication techniques are relatively complicated, inefficient, and time-consuming. In this work, we introduced a simple, efficient and rapid concept to fabricate porous polydimethylsiloxane (PDMS) nanocomposites. PDMS nanocomposites with various porous structure were produced within a few minutes through just one-step microwave irradiation without any post-processing. Three solvents with different boiling points were selected as sacrificial materials to control porous structure. To fabricate nanocomposites, BaTiO3 (BT) nanoparticles were mixed into the uncured PDMS and sacrificial solvent mixture. Additionally, Ni nanoparticles were also used to understand the effect of embedded material’s property on porous structure. The porous BT/PDMS nanocomposites fabricated via microwave irradiation greatly enhanced the electrical performance of TENGs as compared to a pure solid elastomer. The present study provides a simple, rapid and inexpensive approach for fabricating TENGs based on porous elastomeric nanocomposites.

In this study, we investigated geometrical characteristics of the inkjet-printed lines with non-zero receding contact angle (CA) on plasma-treated substrates in terms of various printing variables and analyzed the fluidic behavior and hydrodynamic instability involved in the line formation process. The printing variables included surface energy, droplet overlap ratio, printing frequency, a number of ink droplets, substrate temperature and printing procedures. For the study, a colloidal suspension containing 56 wt % silver nanoparticles in tetradecane solvent was used as a printing ink. It has electrical resistivity of 4.7 μΩ·cm. The substrates were obtained by performing a plasma enhanced chemical vapor deposition (PECVD) process with C4F8 and O2 under various treatment conditions. As results of the experiments, the surface shape and pattern of the inkjet-printed Ag lines were dominantly influenced by the surface energy of the substrates, among the printing variables. Accordingly even when the receding CA was non-zero, bulging instability of the lines occurred forming separate circular patterns or regular bulges connected by ridges. It is a new finding of this study, which is completely different with the bulging instability of inkjet lines with zero receding CA specified by previous researches. The bulging instability decreased by increasing surface temperature of the substrates or employing interlacing procedure instead of continuous procedure for printing. The interlacing procedure also was advantageous to fabricate thick and narrow Ag lines with well-defined shape through overprinting on a hydrophobic substrate. These results will contribute greatly to not only the production of various printed electronics containing high-aspect-ratio structures but also the improvement of working performance of the devices.

In this study, we investigate the evaporation behavior of inkjet-printed semiconductor layers of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) to obtain well-oriented crystalline structures for the fabrication of high-performance organic thin film transistors (OTFTs). Variations in overlap and substrate temperature are considered to control the evaporation behavior and the resulting crystalline structures of the layers. The internal flow and corresponding contact line movement can be controlled via three representative inkjet-printing regimes. For inkjet-printing regimes that induce outward convective flow (the coffee stain effect), randomly-oriented TIPS pentacene crystalline structures are produced by irregular contact line receding. With an optimized inkjet-printing regime, uniform bottom contact line movement is generated by the unidirectional internal flow, resulting in well-oriented crystalline structures. All-inkjet-printed OTFTs with semiconductor layers inkjet-printed using the optimized regime exhibit a high field effect mobility of ~ 0.13 cm 2 /Vs, due to the one-dimensionally-oriented TIPS pentacene crystal arrays.

In this study, the evaporation behavior and the resulting morphology of inkjet-printed dielectric layers were controlled using a mixed-solvent system to fabricate uniform poly-4-vinylphenol (PVP) dielectric layers without any pinholes. The mixed-solvent system consisted of two different organic solvents: 1-hexanol and ethanol. The effects of inkjet-printing variables such as overlap condition, substrate temperature, and different printing sequences (continuous and interlacing printing methods) on the inkjet-printed dielectric layer were also investigated. Increasing volume fraction of ethanol (VFE) is likely to reduce the evaporation rate gradient and the drying time of the inkjet-printed dielectric layer; this diminishes the coffee stain effect and thereby improves the uniformity of the inkjet-printed dielectric layer. However, the coffee stain effect becomes more severe with an increase in the substrate temperature due to the enhanced outward convective flow. The overlap condition has little effect on the evaporation behavior of the printed dielectric layer. In addition, the interlacing printing method results in either a stronger coffee stain effect or wavy structures of the dielectric layers depending on the VFE of the PVP solution. All-inkjet-printed capacitors without electrical short circuiting can be successfully fabricated using the optimized PVP solution (VFE = 0.6); this indicates that the mixed-solvent system is expected to play an important role in the fabrication of high-quality inkjet-printed dielectric layers in various printed electronics applications.

Paper and pencil have many advantages in triboelectric nanogenerators (TENGs) in terms of low-cost, light weight, and environment friendliness. In this work, a pencil-on-paper triboelectric nanogenerator (PP-TENG) with highly enhanced performance was introduced. In order to use paper as a friction layer and improve its triboelectric performance, a simple and rapid paper-coating process was utilized with polyvinylidene fluoride (PVDF), polyvinyledenedifluoride-trifluoroethylene (PVDF-TrFE), and poly(methyl methacrylate) (PMMA) solutions. The fabrication process of the PP-TENG was completed within 10 minutes via pencil drawing of an electrode followed by a solution coating. With an optimized electrode shape, the PP-TENG showed a maximum power density of 64 mW m−2, which is more than 19 times higher than that of the uncoated paper TENG. The electrical performance of the PP-TENG was sufficient to drive a few hundred LEDs and charge various capacitors. It was maintained after the paper was folded or even crumpled. The proposed PP-TENG is expected to be utilized with other wearable electronic devices.

This work aims to present a flexible, highly sensitive, capacitive pressure sensor based on an elastomeric dielectric layer with uniformly distributed micro-pores. The porous dielectric layer was simply produced by microwave treatment of polydimethylsiloxane (PDMS) mixed with a sacrificial solvent within a few minutes. The pressure sensor using a porous PDMS dielectric layer fabricated with 40 wt% sacrificial solvent had a sensitivity of 0.813 kPa−1, which is 11 times higher than that of the sensor using a non-porous dielectric layer. To further improve the sensitivity, low-cost commercial glass was used as a mold to form microstructures on the surface of the porous dielectric layer. Due to the enhanced deformability, high sensitivity of 1.43 kPa−1 and a fast response time of 70 ms was achieved. The performances of a sensor array as well as finger sensors were also demonstrated by placing light-weight objects on the array and holding a plastic cup. It would be expected that the proposed sensors could be utilized in the application of artificial skins or soft robotics.

The electrical sintering characteristics of inkjet-printed line patterns on a paper substrate were investigated by varying initial pattern resistance, input voltage, sintering time, and input voltage profile. The initial resistance was controlled by preheating the patterns, and its range was between 500 Ω and 5 MΩ. Depending on the input voltage and initial resistance, there exist three different regions: sintering, no change, and blowout. While no sintering is observed for too high initial resistance, blowout of printed lines occurs for a larger input voltage. For the initial resistance lower than ~ 100 kΩ and the input voltage ranging from 20 V to 40 V, all the printed lines are electrically sintered within a short time without damaging the underlying paper substrates. When using the two-step voltage profile, the final resistance of lines becomes five times smaller than the resistance with the one-step voltage profile due to the increase in the grain size and the reduction in the void area, and no burning or blowout occurs in the lines. Due to its many advantages, the electrical sintering can provide a fast, reliable and effective way to fabricate high quality inkjet-printed conductive patterns for various printed electronics applications.

We have obtained a wide range of surface wettabilities of PI substrate for inkjet printing by combining hydrophobic solution coating and O 2 or Ar plasma treatments. Experiments were conducted to investigate the variation in inkjet-printed dot diameters with different surface treatments. The change in chemical and physical characteristics of treated surfaces was evaluated using static contact angle measurements, field emission scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Only hydrophobic coated surface produces the smallest dot diameter and the largest contact angle. Dot diameter increases and contact angle decreases as the plasma treatment time increases. Since the removal of hydrophobic layer from the surface occurs due to the etching effect of O 2 and Ar plasma during the plasma treatments, F/C ratio decreases with increasing the plasma treatment time. Surface roughness variations are also observed after plasma treatments. The ranges of printed dot sizes for O 2 and Ar plasma treatments are 38 μm–70 μm and 38 μm–92 μm, respectively. Ar plasma treatment shows a wider range of surface wettability because of higher removal rate of the hydrophobic layer. This combination of hydrophobic coating and plasma treatment can offer an effective way to obtain a wide range of surface wettabilities for high quality inkjet-printed patterns.

In this study, an effective method to fabricate well-defined conductive lines with high resolution has been proposed by combining inkjet printing with soft lithography. Soft lithography techniques such as nano-imprint lithography for negative SU-8 patterns and micro-contact printing for hydrophobic fluorocarbon layer were used to create surface wettability contrasts so that the spreading of droplets was confined on a hydrophilic region surrounded by hydrophobic regions. Surface wettability contrasts were evaluated by water contact angle measurements, and the maximum contact angle difference between hydrophobic and hydrophilic surfaces was 104^o. With the help of such surface wettability contrasts and lift-off process for removing small amount of ink stains, well-defined inkjet-printed lines as narrow as [email protected] can be successfully generated. The sintered Ag lines also show good electrical resistivity of [email protected]@W.cm, 4.7 times as large as bulk Ag's resistivity. This combined approach can be used to fabricate high-quality, high-resolution electrodes in printed electronics applications.

The objective of this work is to demonstrate the feasibility of inkjet-printed passive components. All passive components such as resistor, capacitor and inductor were inkjet printed on a polyimide (PI) substrate with various functional inks. For the insulator layer, poly-4-vinylphenol (PVP) and cross linking agent (poly(melamine-co-formaldehyde)) were dissolved in an ethanol. A mixture of poly(3,4-ethylene dioxythiophene) doped with polystyrene sulfonated acid (PEDOT:PSS) and ethylene glycol was used to print a resistor. Barium titanate (BaTiO"3) and soft ferrite (Ni-Zn) powders were added to the synthesized insulator solution to improve its dielectric and magnetic characteristics, respectively. An RC circuit was also fabricated based on the results of the printed passive components. The printed electric components and circuit were characterized using LCR meter, function generator and digital oscilloscope. The measured responses of the printed RC circuit were in good agreement with estimated results.

Well-defined cell patterns, including both adherent and non-adherent cells, were created using piezoelectric inkjet printing of a cell membrane-anchoring polymer composed of a hydrophobic oleyl group, a hydrophilic poly(ethylene glycol) (PEG) chain, and an amino-reactive N-hydroxy-succinimide (NHS) end group. Various complex living cell patterns were created by surface engineering in which inkjet-printed, membrane-anchoring polymer patterns controlled the geometric distributions of immobilized cells. Non-adherent (SNU-620) and adherent cells (HeLa) were stably anchored and patterned on a glass substrate through interactions between cell membranes and the hydrophobic oleyl groups. The effects of an apoptosis inducer (staurosporine) and an anticancer drug (paclitaxel) were visualized on cells immobilized on the polymer-printed patterns. This approach may have broad utility in most advanced biomedical devices requiring miniaturized and precisely controlled living cell patterns.

The configuration of automated polishing systems requires the implementation of monitoring schemes to estimate surface roughness. In this study, a precision polishing process – magnetic abrasive finishing (MAF) – was investigated together with an in-process monitoring set-up. A specially designed magnetic quill was connected to a CNC machining center to polish the surface of Stavax (S136) die steel workpieces. During finishing experiments, both acoustic emission (AE) signals and force signals were sampled and analyzed. The finishing results show that MAF has nanoscale finishing capability (up to 8nm in surface roughness), and the sensor signals have strong correlations with parameters such as the gap between the tool and workpiece, feed rate, and abrasive size. In addition, the signals were utilized as input parameters of artificial neural networks (ANNs) to predict generated surface roughness. To increase accuracy and resolve ambiguities in decision making/prediction from the vast amount of data generated, sensor data fusion (AE + force)-based ANN and sensor information-based ANN were constructed. Among the three types of networks, the ANN constructed using sensor fusion produced the most stable outcomes. The results of this analysis demonstrate that the proposed sensor (fusion) scheme is appropriate for monitoring and prediction of nanoscale precision finishing processes.

The paper aims to investigate the influence of C 4 F 8 plasma treatment on the inkjet-printed dot sizes on flexible PI substrates using the response surface method. The whole experimental region of two independent variables was divided into a number of sub-domains to estimate the accurate relationship between the independent variables and the response. From the RSM analysis, desired dot diameters ranging from 30 μm to 70 μm could be obtained by selecting the proper combination of the RF power and gas pressure. The chemical and physical changes in plasma-treated surfaces were also characterized by contact angle measurements, scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. The results show that both RF power and gas pressure have a significant influence on the dot diameter. In some experimental region, well-defined dots cannot be produced due to unstable plasmas. The dot diameters on the plasma-treated surfaces are well correlated with the contact angles on them. The roughness and F/C ratio of surfaces are also affected by the plasma treatment. The plasma condition yielding higher F content results in more hydrophobic surfaces.

This paper aims to investigate the effects of the substrate, the printed line thickness and the sintering temperature on the electrical resistivity, Young's modulus and hardness of inkjet-printed Ag thin films. Electrical resistivity was determined from the four-point method and Young's modulus and hardness were evaluated from nanoindentation test. Several models for evaluating Young's modulus and hardness were used and compared to account for the influence of substrates. It is noted that Ag lines on glass have higher resistance and resistivity than those on polyimide (PI) since Ag lines on glass and PI have tensile and compressive residual thermal stresses, respectively, due to the difference of coefficient of thermal expansion between Ag lines and substrates. Young's modulus of Ag films on glass can be predicted by the modified King and Bec models considering the substrate effect, but these models offer unstable results for Ag films on PI. Young's modulus and hardness of Ag films increase with the sintering temperature, and they are little affected by the film thickness when fully sintered.

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Six composite sensors were prepared by casting a solution of different polymers and conductive carbon black nanoparticles on a glass substrate with two comb-shape Au electrodes. The chemoresistive response and background noise level were measured as a function of concentration upon exposure to various breath biomarker compounds: acetic acid, toluene, ethanol, acetone, n -pentane, and isoprene. All sensors exhibited a good linear response with respect to concentration, suggesting a typical volumetric transduction mechanism. Limit-of-detection (LOD) values were determined by an extrapolation of the linear relationship and were found to be in the range of 80 ppb to 240 ppm, demonstrating the potential of highly sensitive detection for the biomarkers. The LOD variation can be roughly interpreted in terms of the difference in boiling temperature of an analyte in a physisorption-based model; the higher boiling temperature results in a lower LOD due to a strong tendency toward condensation. The LOD values were observed to become two or three orders of magnitude smaller by exploiting specific chemical interactions between the polymers used and the analyte.

We investigated electrical properties of inkjet-printed Ag lines by varying the substrate, dimension of lines and sintering temperature. The effect of cracks developed in the lines during drying and sintering was also examined. The results show clear evidence of a strong crack and substrate effect on electrical properties of printed Ag lines. The crack formation is clearly dependent on the dimension of lines. Crack network occurs and becomes more pronounced for wider and thicker lines. Even without the crack formation, the resistance and resistivity of lines on glass are higher than those on polyimide due to residual thermal stresses.

We investigated the effects of surface wettability, substrate temperature, and overprinting on the shapes and morphologies of dried and sintered inkjet-printed dots of nanosilver suspensions. The surface wettability was modified by two different plasma surface treatments: C 4 F 8 plasma treatment for hydrophobic surface and O 2 plasma treatment for hydrophilic surface. The substrate temperature was varied from 25 to 85 °C with an interval of 20 °C. In order to change the dot thickness, dots were overprinted up to three times after complete drying of the ones previously printed. Printed dots were sintered for 1 h at 210°C. The shapes and morphologies of dried dots including both single and overprinted dots were strongly influenced by the surface wettability of the substrate. The cross-sectional profile was more convex on the hydrophobic surface at lower substrate temperature, but stack-like morphologies of overprinted dots were obtained on both surfaces at higher substrate temperature due to the fast evaporation of solvent and coffee ring effect. Dots on hydrophilic surfaces experienced more shrinkage after sintering, and the shrinkage ratio of sintered dots tended to decrease with an increase in the number of overprints. The microstructure of sintered dots showed that nanoparticle clusters were more closely packed on hydrophobic surfaces.

The effect of droplet/substrate interactions on the geometrical characteristics such as shape and morphology of as-printed conductive lines of nanosilver suspensions was investigated by varying the surface energy, substrate temperature and droplet spacing. With a plasma surface treatment using a mixture of C 4 F 8 and O 2 gases, various surface wettability conditions were obtained that could produce desired droplet diameters on the substrate from 30 μm to 70 μm. The substrate temperature varied from room temperature to 75 °C, and ink droplets ejected from a 30 μm nozzle were printed with various overlaps from 10% to 60%. When printed at room temperature, continuous lines are not formed due to line instability issues such as merging of neighboring droplets and line bulges. By heating the substrates, continuous lines without bulges could be obtained on the relatively hydrophobic substrate because the heat flux from the substrate enhances the evaporation rate of the solvent. The coffee ring effect in the droplets and lines is more enhanced as the substrate temperature increases. This effect is weaker in the lines than in the single droplets due to less edge length in the lines. Under appropriate conditions, well-defined continuous lines could be printed without coffee rings.

This study focuses on investigating the effects of adherend materials on the torsional strength of composite tubular adhesive joints. The initial failure index was introduced to consider the effect of residual thermal stresses. Two different composite adherends were considered in this analysis: carbon/epoxy and glass/epoxy. The effects of stacking angle and adhesive thickness on joint strength were also investigated. The results show that the joint with the carbon/epoxy adherend is more affected by the residual thermal stresses. The failure mode and joint strength depend on the stacking angle and adhesive thickness as well as the adherend materials.

The nonlinear analysis of tubular single-lap adhesive joints with composite adherends was performed by incorporating the nonlinear behavior of the adhesive into the analysis. For this purpose, the stress and strain in the laminated composite tube were first calculated under a general loading scheme, and then the iterative solution of the joints was derived by including the nonlinear properties of the adhesive. The stress distributions in the adhesive were investigated for different types of composite adherends and compared with the results of the linear analysis. The effect of the bonding length on torque transmission capability was also taken into consideration. The results indicate that the nonlinear analysis relieves the stress concentration at the edge of the joint, resulting in a more accurate prediction of joint strength.

Combined thermal and mechanical analyses were used to investigate the effect of joint design parameters such as the adhesive thickness and bonding length on stress distributions and torque capacities of tubular adhesive joints with composite adherends. The finite element analysis was employed to calculate the residual thermal stresses due to fabrication, and the mechanical stresses were analyzed using the nonlinear analysis of tubular adhesive joints. The analyses reveal that the stacking angle, adhesive thickness and bonding length have a significant influence on residual thermal stresses, and consequently failure modes and joint strengths.

A 3-D transient heat transfer finite element (FE) analysis was performed to simulate the curing process of thick thermoset composites. The simulated temperature was compared with the available experimental data to check the validity of the analysis. The influence of thickness of composite laminates on the temperature distribution was investigated, and how the size of laminates affects the inside temperature was also discussed. The results indicate that the laminate thickness rather than the laminate size has a significant influence on temperature distribution, and the 3-D analysis offers more accurate predictions than the 1-D analysis.

Since the performance of joints usually determines the structural efficiency of composite structures, an extensive knowledge of the behavior of adhesive joints and the related effect on joint strength is essential for design purposes. In this study, the torque capacity of adhesive joints was predicted using the combined thermal and mechanical analyses when the adherend was a composite tube. A finite element analysis was performed to evaluate residual thermal stresses developed in the joint, and mechanical s stresses in the adhesive were calculated including both the nonlinear adhesive behavior and the behavior of composite tubes. Three different joint failure modes were considered to predict joint failure: interfacial failure, adhesive bulk failure, and adherend failure. The influence of the composite adherend stacking angle on the residual thermal stresses was investigated, and how the residual thermal stresses affect the joint strength was also discussed. Finally, the predicted results were compared with experimental results available in literature.

A three-dimensional finite element analysis is performed to investigate the effects of fiber arrangements on the residual thermal stresses in unidirectional composites of various fiber volume fractions (FVFs). The fiber arrangements include the regular fiber arrays (square and hexagonal arrays) and a random fiber array. Normal, tangential, and shear stresses at the fiber–matrix interface are first obtained using unit cells of the regular square and hexagonal fiber arrays. To simulate better real fiber arrangements, random fiber distribution is modeled and analyzed using a finite element analysis. Statistical distributions of residual thermal stresses are obtained for various FVFs and compared with the results from regular fiber arrays. The effects of constituent material properties of composites on thermal stresses are also taken into consideration. The results indicate that the random arrangement of fibers has a significant influence on residual thermal stresses especially at high FVFs. The mode stresses of the random fibers are well estimated using the square array whereas the mean stresses are better predicted from the hexagonal array. It is shown that predicted coefficients of thermal expansion are not influenced by the microstructure of composites.

The conventional manufacturing of composite sandwich structures is completed by adhesive joining separately prepared composite faces to cores. The joining process during sandwich fabrication is most difficult process, which requires strict quality control. The joining process can be eliminated when the sandwich structures are manufactured by co-cure method inside a mold using the large coefficient of thermal expansion (CTE) of foam cores. In this work, the foam core composite sandwich beams were manufactured inside a mold using the pressure generated due to the difference of CTEs between the mold and the foam. Considering the non-linear thermal expansion properties of foam during co-cure manufacturing, the pressure generated inside the mold was analyzed and calculated. In addition, the calculated pre-compression strain was given to the foam core sandwich beams for enough consolidation of the composite faces.

An electrohydrodynamic (EHD) patterning method was utilized to obtain high-resolution line patterns in a low electric field regime without an additional mechanical drawing process. Molecular weight and weight percent of a polymer were selected as key parameters to reduce the voltage. EHD patterning was performed using polyethylene oxide (PEO) solutions. The threshold voltages (V th) to initiate jet ejection are almost the same for all solutions. A method verified in this study, reducing the driving voltage (V d) just after the initiation of the jet at the threshold voltage, can make a very thin, continuous jet, while increasing molecular weight and weight percent were enabled to further reduce the input voltage. As the voltage reduction ratio (V d/V th) is decreased, the jet behaves like a solid rather than a liquid due to its fast solidification. The line width of the resultant line pattern could be tuned from 50 nm to 10 μm depending on the substrate moving speed. Contour maps were also developed that show the pattern mode variation as a function of the voltage reduction ratio and key parameters. The results show that well-defined PEO line and grid patterns can be fabricated via the proposed EHD direct patterning under appropriate conditions.

Recently, robot structures handling liquid crystal display (LCD) glass panels are increased in size as the size of LCD is increased. In order to handle large LCD panels, the robot structures should have high stiffness to reduce the deflection of robot end effector under the weights of LCD. The LCD manufacturing industries have a trend to employ double arm type robots rather than single arm type robots to increase productivity. Currently, two aluminum wrist blocks that have different configurations not to interfere with each other are mounted on the robot arms. The aluminum wrist block becomes one of the largest deflection sources as the size of the robot structures increases. Since the size of the wrist block can not be increased indefinitely to increase the stiffness due to the limitation of driving motor power, the best way to increase the stiffness of the wrist block is to employ carbon fiber epoxy composite material for structural material of the wrist block because the carbon fiber epoxy composite material has much higher specific stiffness and damping than aluminum. In this work, the two wrist blocks for the double arm type robot for handling large LCD glass panels were designed and manufactured using foam core sandwich structure. Finite element analysis was used along with an optimization routine to design the composite wrist blocks. Box type sandwich structures were employed to reduce shear effect arising from the low modulus of polyurethane foam core. The weight reduction of the composite wrist blocks was more than 50% compared to those of comparable aluminum wrist blocks and found that the composite wrist blocks had much improved performances compared to those of the aluminum wrist blocks from the static and dynamic tests.

Duringthe curingprocess of thick glass/epoxy composite laminates, substantial amounts of temperature lagand overshoot at the center of the laminates is usually experienced due to the large thickness and low thermal conductivity of the glass/epoxy composites, which require a long time for full and uniform consolidation. In this work, the temperature profiles of a 20mm thick unidirectional glass/epoxy laminate duringan autoclave vacuum bag process were measured and compared with the numerically calculated results. For the calculation of distributions of the temperature, degree of cure, resin pressure, exothermic heat and required time for full consolidation by three-dimensional finite element analyses, the effects of convective heat transfer coefficient and geometry of mold and bagging assembly on the temperature profiles were taken into consideration. Based on the numerical results, an optimized cure cycle with the coolingand reheatingsteps was developed by minimizingthe objective function to reduce the temperature overshoot in the composite. From the experimental and numerical results, it was found that the measured temperature profiles were in good agreement with the numerical ones, and conventional cure cycles recommended by prepregmanufacturers for thin laminates should be modified to prevent temperature overshoot and to obtain full consolidation.

Highly sensitive capacitive pressure sensors with poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) dielectric layers were prepared. The dielectric layers were directly produced by electrospinning P(VDF-TrFE) nanofibers for various spinning times. A longer spinning time enhanced the deformability of the electrospun P(VDF-TrFE) layers, resulting in higher sensitivity owing to larger changes in the deformation of the dielectric layer. One of the capacitive pressure sensors showed a high sensitivity of 2.81 kPa−1 at a pressure ≤ 0.12 kPa, a good response time of 42 ms, and small hysteresis. The sensitivity of the sensor was five times higher than that of a typical capacitive pressure sensor. The fabricated pressure sensor could detect a tiny water droplet as light as 7 mg. It is expected that the electrospun P(VDF-TrFE) nanofibers can be used as sensing materials for highly sensitive pressure sensors in wearable electronics applications.

During the wire cutting process, the moving wire is usually supported by a cantilever arm and wire guides. As the traveling speed of the wire has been increased in recent years to improve productivity, vibration of the cantilever arm occurs, reducing the positional accuracy of machining. Therefore, the design and manufacture of a cantilever arm with high dynamic characteristic materials have become important as the machining speed increases. In this work, a cantilever arm for guiding the moving wire was designed and manufactured using carbon fiber epoxy composite in order to improve the dynamic characteristics of machining, because composite materials have high specific stiffness, high specific strength and high damping capacity. Experiments and finite element analyses were conducted to investigate the effect of the joining length of the steel flanges on the load capacity. The static and dynamic characteristics of the fabricated composite cantilever arm were compared with those of the conventional cast-iron cantilever arm. From the results, it was found that the developed composite cantilever arm had better dynamic characteristics compared to the conventional arm.

A heddle (or heald) frame is the major part of a loom that produces woven cloth by insertion of weft yarns between warp yarns. Warp yarns are manipulated by many heddles fixed in a heddle frame. Recently, the up and down speed of heddle frames has been increased much for the increase of productivity, which induces higher inertial stresses and vibrations in the heddle frame. Conventional aluminum heddle frames have limits for the speed increase due to their low fatigue flexural strength as well as low bending stiffness. The estimated fatigue life of the aluminum heddle frame was 6 months at 600 rpm and infinite at 400 rpm, which was the same results reported by textile industries. Since carbon fiber epoxy composite materials have high specific fatigue strength (S/ρ), high specific modulus (E/ρ) and high damping capacity, in this paper a composite heddle frame was designed and manufactured. The optimum box type cross-sectional shape of the heddle frame and stacking sequence were determined by finite element analysis. The box type composite structure with several ribs was manufactured with prepregs by the autoclave vacuum bag process. Then the static and dynamic characteristics of the composite heddle frame and the aluminum heddle frame were measured and compared.